The present invention relates to a transmission system comprising a data communication device coupled to a first wireless terminal, the wireless terminal being arranged for communicating with a second wireless terminal comprising a network interface for coupling the second wireless terminal to a communications network.
The present invention is also related to wireless terminals for use in such a system.
A transmission system according to the preamble is known from U.S. Pat. No. 5,353,334.
Such transmission systems can e.g. be used for connecting personal computers to a telephone network without needing to be in the vicinity of a wired connection to such a telephone network. This is in particular desired for portable computers such as laptops and hand held computers such as the Philips Velo computer. These computers can have integrated or insertable data communication devices such as modems or ISDN terminal adapters for accessing a telephone network. To be able to access the telephone network without needing to be in the vicinity of a wired connection to such a telephone network, a wireless link to said telephone network is necessary.
The above mentioned US patent discloses a wireless phone to which a voice-band modem can be connected. For the connection to the wireless phone a so-called signal processing cable is used which comprises an interface for interfacing the voice band modem to the wireless phone.
For use with this interface, the voice band modem should provide on separate terminals the modulated data signal to be transmitted and digital control information for control purposes such as call set up and dialing. Consequently the data communication device can not be a standard communication device which are available for low prices, but it needs to be a special device dedicated for use with a wireless communication device which are more expensive than the standard communication devices.
It is an object of the present invention to provide a transmission system according to the preamble in which standard data communication devices can be used.
To achieve said purpose, the transmission system according to the invention is characterized in that the combination of the first wireless terminal and the second wireless are arranged for transparently transmitting signals received from the data communication device to the communications network.
By passing the signals from the data communication device transparently to the communication network, the separate connections for transmitting control information to the (first) wireless terminal can be dispensed with. All control information such as dialing is passed directly to the network. If the data communication device is idle, there will be no connection of the second wireless terminal to the communication network.
If the data communication device goes off-hook, this is signaled by the first wireless terminal to the second wireless terminal, which causes its interface to the communication network also to go off-hook. The information received from the communication network, such as a dial tone is transmitted by the second wireless terminal to the second wireless terminal which passes it unchanged to the communication device. The (analog) dialing signals transmitted by the data communication device are transmitted by the first wireless terminal to the second terminal which passes the dialing signals unmodified to the telephone network.
After a connection has been established, the first and second terminals transmit the information received from the data communication device unchanged to the communication network and vice versa. If the data communication device goes on-hook this condition is also signaled by the first wireless terminal to the second wireless terminal which will caus its interface to network also to go on-hook.
An embodiment of the invention is characterized in that the first wireless terminal and the second wireless terminals comprise telephone terminals, the first wireless terminal comprises detection means for detecting whether there is a data communication device connected to it, and switching means for switching, in case a data communication device is connected to the first wireless terminal, the first wireless terminal and the second terminal from a telephony mode into a transparent transmission mode for transmitting the signals from the data communication device to the communications network.
It is convenient to combine the wireless terminals with a telephone function. In this way a multifunctional device is obtained without a large increase of costs, because the majority of the functions of the wireless terminals are necessary both in the telephony mode and in the transparent transmission mode. The presence of a data communication device is determined by the detection means which control a switching means to set the terminals in transparent transmission mode.
The detection means can be constituted by a switch integrated with a connector for a plug of the data communication device. This switch is activated when a plug of a data communication device is inserted into the connector. It is also possible that the presence of a data communication device is only signalled to be present when it goes off hook.
A further embodiment of the invention is characterized in that the first and second wireless terminals comprise digital transmission means for transmitting digitized voice signals, in that the digital transmission means comprise additional error protecting means, and in that the switching means are arranged for activating the additional error protection means in case a data communication device is connected to the first wireless terminal.
In digital cordless telephone systems such as DECT, the digital channel has in general a Bit Error Rate of 10xe2x88x923-10xe2x88x924. In the case the wireless terminals are used in transparent mode, this Bit Error Rate is much too high, because reliable transmission in transparent transmission mode requires a Bit Error Rate smaller than 10xe2x88x926. In order to be able to obtain the low Bit Error Rates in the transparent transmission mode using the same transmission medium as in telephony mode, additional error protection means are activated when the wireless terminals are in transparent transmission mode. These additional error protection means can e.g. comprise a rate ⅓ convolutional encoder in the transmitting part of the wireless terminals, and a rate ⅓ convolutional decoder in the receiving part of the wireless terminals.